The detector consists of 42 BaF2 crystals of 15 cm length.
Covering the full solid angle without any gaps requires two different crystal
shapes, which can be seen in the figure. The shapes of the crystals are
optimized in a way that they all cover the same solid angle, although they
have different shapes.

Figure: The detector is composed of 12 crystals of
type A (red), 30 crystals of type B (green).

Table: Dimensions of the different crystal shapes for
a 4 array of unit radius.See figure before for definitions of the linesegments.

The volumes described above can be arranged to form a closed sphere
with an inner radius of 10 cm and an outer radius of 25 cm. In the present
situation, however, the crystals were moved outwards by 0.335 cm and the
resulting gaps of 2 mm between the crystals were filled 0.1 mm aluminum
foil, 0.5 mm Teflon and 0.4 mm air surrounding. These materials are used
to reflect the scintillation light at the surfaces and to isolate each
crystal from its neighbors. The front of the crystal is also covered with
aluminum and Teflon. The following picture shows the detector with all
crystals in an opened position.

The neutrons reach the sample, centered in the BaF2 crystal
ball, after 80 cm flight path. The crystal nearest to the Lithium target
(neutron production) is replaced by lead in order to absorb -
rays as well collimate the neutrons. The opposite crystal contains a clyndrical
whole of 5 cm diameter.